Man-made consolidated boards include hardboard, chip board, particle board, panel board, acoustical board, insulation board and the like. The uses of such boards depend upon the physical characteristics, such as the density of the board and any exterior embossing or decorative effect applied thereto.
There are two principal processes for the manufacture of man-made boards--the wet process and the dry process. In the wet process, the raw material is uniformly blended in a head box with copious quantities of water to form a slurry. The slurry is deposited onto a water-pervious support member, generally a Fourdrinier wire, where much of the water is removed leaving a wet mat of cellulosic material. The wet mat is transferred from the pervious support member and consolidated under heat and pressure to form the board. The dry process is similar to the wet process except that the cellulosic fibers are first coated with a thermosetting resin binder, such as a phenolformaldehyde resin, and are then randomly distributed into a mat by distributing the resin-coated fibers onto a support member.
The process of embossing a wet or dry mat in a platen press with a heated embossing plate is well known, especially in the manufacture of fiberboards, such as hardboard. An embossing plate is made with a surface contour or protrusions of a desired design, such as wood graining. The heated embossing plate is pressed against the surface of the wet mat under sufficient pressure to impress the plate design into the surface of the panel and thereby consolidate the wet mat into a decorative man-made board having varying thicknesses. The fiberboard mat that is hot-pressed, as inserted into the press, has a uniform thickness and a uniform basis weight. During hot-press embossing, areas of the fiberboard mat adjacent to the embossing plate protrusions necessarily become more compressed than flat or planar areas surrounding the embossed areas, and the consolidated, embossed product is, therefore, more dense at the embossed area.
The bonding necessary for cohesion and strength in a man-made board occurs during the consolidation of the board. Prior to hot-pressing, the loosely disassociated cellulosic fibrous mat is quite weak, but after hot-pressing the mat into its final configuration, it is very powerfully held together by the bonding which occurs during hot-pressing. Hot-pressing during consolidation causes a welding or coalescing of the cellulose fibers at the surface of the product so that the surface portion consists of wood remade in modified form.
The present invention is directed to a method of manufacturing a consolidated, structural panel by hot pressing a wet or dry fibrous mat in a heated press, against a back surface die that includes a plurality of upwardly extending projections to provide fiber-void regions in the back surface of the panel, for material savings and to provide lateral flow of fibers to aid in maintaining more uniform density throughout the panel. The panel thus consolidated has a relatively uniform density throughout its thickness due to lateral flow of fibers, as the fibers slide around an outer surface of the back surface die projections as the projections are pressed upwardly into the back surface of the structural panel. A more uniform density is achieved during consolidation, with die projections inserted into the back surface of the panel, since lateral compressive forces, generated as a result of the surface angle of the die projections, are substantially equal to the compressive force normal to the dies surfaces, as shown in FIG. 2. Forces on the fibers, as the die projections are forced in the mat, can be likened or modeled by compressible springs, A, B and C. As fiber is compressed in a normal (to die) direction the fiber will slide down the face of the pins until the lateral compressive force in the fibers between the projections, as indicated by compression of spring C, produces a balancing force. Adjustment of projection angle, .alpha., allows adjustment of the ratio of normal compression to lateral compression forces, and will allow for compensation for frictional effects from the outer projection faces.
The prior art includes the use of blades or pointed projections and the like, to tenderize or to provide a decorative surface to lumber and to densify weaker areas of consolidated fiberboards. The following patents are examples of tenderizing or decorating wooden articles: Voigt U.S. Pat. No. 839,680; Campbell III, et al. U.S. Pat. No. 3,231,455; and Clarke, et al. U.S. Pat. No. 4,790,360. This Assignee's Rinker U.S. Pat. No. 5,614,231, teaches that rigid fiberboard mats can be compressed into embossed door facings using a "push", or door panel embossed design, to provide denser areas in sharply embossed design areas to prevent "soft" edges. This Assignee's Beuving, et al. U.S. Pat. No. 5,129,435 discloses cutting incisions into a fiberboard mat, prior to hot press consolidation thereof, to condition the mat, by disrupting the fiber network and make the fibers more pliable. However, since the fibers are not held in any particular disrupted location during consolidation of the mat, in accordance with the Beuving, et al. process, substantially better density uniformity is not achieved.